1. Field of the Invention
This invention relates to a testing apparatus for an item in sheet form, and in particular to such testing apparatus provided with a measuring system having a light source and a photosensitive detector.
Such testing apparatus is advantageously used in bank note acceptors such as those used in automatic service machines.
2. Description of the Prior Art
Testing apparatus of this kind is known from U.S. Pat. Nos. 3 761 876 and 4 319 137, in which a bank note is optically scanned line by line by means of a linear array of a plurality of detectors. Each line is broken down into an equal number of picture elements, in accordance with the number of detectors. It is also known from U.S. Pat. No. 4 319 137 that the items which are judged genuine may also have patterns from a predetermined set, and that the items are transported by means of endless belts.
Swiss Patent Specification No. 661 603 describes a transport system which provides for careful transportation of bank notes of different sizes by means of endless belts.
It is also known from European Patent Application Serial No. 109 490 for only small surface portions of the bank note to be examined in a reflection mode, in order to detect soiling of or damage to the bank note.
European Patent Application Serial No. 198 819 describes a method in which the light which experiences a spectral variation due to the entire surface of the bank note in a transmission or a reflection mode is analyzed by at least one detector in order to establish the authenticity of the bank note, irrespective of its position in the testing device.